Landslide, Thistle, Utah

R.L. Schuster U.S. Geological Survey

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This landslide began moving in the Spring of 1983. The event was in response to ground water buildup from heavy rains the previous September and the melting of deep snow pack for the Winter of 1982-1983. Within a few weeks, the landslide dammed the Spanish Fork River, obliterating U.S. Highway 6 and the main line of the Denver and Rio Grande Western Railroad. Flood waters rose behind the landslide dam; the town of Thistle was inundated and destroyed. Total costs (direct and indirect) exceeded $400 million. This was the most costly single landslide event in U.S. history.

The slopes above streams and rivers are subjected to a variety of processes that cause them to recede and retreat from the river or stream channel. These processes, collectively called mass wasting, can be classified according to rapidity of movement and according to the type of materials that are transported.